JPH01277337A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide the recording medium which has the long-period preservable property of recording and high-speed erasing property of recording in combination by providing a recording layer consisting of an alloy having a specific compsn. to said medium. CONSTITUTION:The recording layer consisting of the alloy having the compsn. expressed by the formula SbxTe1-x (0.4<=x<0.7) is provided. The Sb-Te alloy constituting the recording layer consists of 40-70atomic%, more preferably 45-65atomic% Sb and the balance the element Te. The recording layer having the long-period stability of the good writing state, the high-speed erasing property and the repetitiveness of writing-erasing in combination is not obtainable if the content of the Sb is below 40atomic%. The recording medium well provided with the required characteristics such as the long-period preservable property of the writing state, the high-speed erasing property and the repetitiveness of the writing-recording is thereby obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical recording medium, and in particular to an optical recording medium suitable as a rewritable laser optical recording medium with improved long-term stability and high-speed erasability of recorded information. Regarding the medium.

[Conventional technology]

In recent years, with the advancement of compact and high-performance lasers, recording media that record information on a thin metal film provided on a substrate by irradiating focused laser light have enabled high-density, large-capacity recording. It is expected as such. Among these, rewritable laser beam recording media, which perform recording based on the amorphous-crystalline transition of a thin metal film, write information by heating the thin metal film with laser light to above its melting point and then rapidly cooling it to become amorphous. In addition, the information is erased by heating the thin metal film with a laser beam to a temperature above its melting point and then slowly cooling it to crystallize it.The writing and erasing of information can be repeated many times. It is attracting particular attention because of its advantages.

With such rewritable laser optical recording media, (a) even when high-speed recording is required, such as with optical discs,
Laser light output 20n+W or less, pulse width 10 when writing
(b) have stable repeatability of writing and erasing (in practical terms, 103
(C) High long-term stability in the written state near room temperature (Practically speaking, it is said to be 10 years or more).

However, a recording medium that combines these required characteristics in a well-balanced manner has not yet been developed.

For example, pure Te has a glass transition temperature around room temperature (approximately 20°
C), and even if it is made amorphous, it easily becomes crystalline in a short period of time, so it cannot be used as a recording layer.
A Te alloy film whose glass transition temperature is increased to 100° C. or higher by adding impurity elements such as s and Bi has been proposed as a recording layer.

[Problem to be solved by the invention]

According to the Te alloy film described above, it is possible to obtain long-term stability of the written state for more than 10 years, but in that case, it takes more than 10 μsec to erase the written state, usually 10 to several hundreds of seconds.
Since it is necessary to irradiate laser light with a pulse width of μsec, high-speed erasing performance is lost.

As described above, conventional rewritable laser optical recording media have a problem in that they do not sufficiently meet the above-mentioned required characteristics.

Therefore, an object of the present invention is to provide a rewritable laser optical recording medium that has the above-mentioned required characteristics in a well-balanced manner. Particularly, it is an object of the present invention to provide a rewritable laser beam recording medium that has both long-term storage properties and high-speed erasability of records.

[Means to solve the problem]

As described above, conventionally, when an impurity element is added to Te and the amount thereof is increased, the long-term stability of the amorphous state is improved, but the crystallization rate is lowered and the high-speed erasing property is lowered. In addition, it was thought that repeated writing and erasing would cause irreversible changes such as phase separation, resulting in a decrease in repeatability. However, the present inventors have surprisingly found that by forming a recording layer with a Te alloy thin film in which sb is added to Te at a much higher concentration than before, a recording medium that can achieve the above object can be obtained. I found it.

That is, the present invention provides the formula: 5bXTe, -.

[Here, X is a number of 0.4≦x<0.7. An optical recording medium having a recording layer made of an alloy having a composition represented by the following is provided.

The Sb-Te alloy constituting the recording layer of the recording medium of the present invention is 40 to 70 atomic %, preferably 45 to 65 atomic % of 5b.
and the remainder is the element Te. If the content of sb is less than 40 at %, it is impossible to obtain a recording layer that has good long-term stability of written state, high-speed erasing performance, and writing-erasing repeatability.

In the recording medium of the present invention, the recording layer is usually formed on the substrate. The method of forming the recording layer is not particularly limited, and for example, a vacuum evaporation method, a sputtering method, etc. can be used. The thickness of the recording layer typically ranges from 200 to 1000 thick.

Examples of the substrate used include synthetic resins such as acrylic resin, polycarbonate resin, and polyimide resin, and glass such as Pyrex glass. The thickness of the substrate typically ranges from 1.2 to 1.5 mm.

In the recording medium of the present invention, the upper and lower surfaces of the recording layer are small (
On the other hand, usually on both sides, in order to prevent perforation or deformation of the recording layer during heating with laser light, or irreversible deformation of the synthetic resin substrate, and to prevent oxidation of the recording layer. Therefore, it is desirable to provide a protective layer (overcoat layer, undercoat layer). Examples of the material of the protective layer include Sing, SiO+ A1zOz+
Y! 03+ wo,, Ta205゜CrzO3+
Cents Mob, Inz03. Gem,
Inorganic oxides such as Ti01+ Zr0z, AIN+ BN
, inorganic nitrides such as 5isNa,'gFz+CeF3
Examples include metal fluorides such as ZnS, metal sulfides such as ZnS, and organic polymer substances such as polyphenylene sulfide, polytetrafluoroethylene, and polyimide. The protective layer made of these inorganic materials can be formed by, for example, a vapor deposition method such as electron beam heating vapor deposition, or a method such as sputtering. Further, the protective layer made of an organic polymer substance can be formed by a method such as vapor deposition or sputtering, and a plasma polymerized film of tetramethyltin or the like can also be used. The thickness of the protective layer usually ranges from 200 to 1500.

-a, since inorganic protective glii has excellent heat resistance, it is difficult to cause irreversible deformation (and is particularly suitable for obtaining recording media with high repeatability of writing and erasing.Organic protective layer) has low thermal conductivity, so there is less energy loss due to thermal diffusion when the temperature of the alloy film of the recording layer is raised above the melting point with laser light (therefore, writing and erasing can be performed with laser light with a shorter pulse width). There are advantages that can be achieved.

When manufacturing the recording medium of the present invention, if a heat-resistant plastic such as highly heat-resistant polyimide or heat-resistant glass such as Pyrex is used as the substrate, there is no risk of deformation of the substrate when heated by laser light. , a protective undercoat layer is not required, which is advantageous in improving repeatability of writing and erasing.

Further, the form of the recording medium of the present invention is not particularly limited, and examples thereof include a disk shape, a card shape, and the like.

[Effect]

In the recording medium of the present invention, the various required characteristics described above are achieved in a well-balanced manner (although the reason why this is achieved is not necessarily clear, the present inventors have found that a Te-Sb alloy with a composition of 40 to 70 at% Sb is 5btTe3 We have discovered that it becomes a single phase, and this makes it possible to repeat writing and erasing in a single phase state. Furthermore, combined with the moderate melting point and crystallization temperature, we have found that It is surmised that the conflicting required characteristics are being improved.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 (1) As a substrate, dimensions 50 mm square and thickness 1.2 mm
Three types of Pyrex glass plates were used: a polycarbonate resin plate with the same dimensions, and a polycarbonate resin disk with a diameter of 130 mm and a thickness of 1.2 mm. First, 5i02 with a film thickness of 150 mm was deposited on one side of these substrates by electron beam evaporation.
A film was formed. Next, on top of that, electron beam heating evaporation method Niyori S
Sb-Te alloy films with a thickness of 1000 atomic % and b contents of 40.45, 50.55.60 and 65 atomic %, respectively, were formed. The deposition was carried out at I
s in the alloy film produced by changing the electron beam output for two evaporation sources of sb and Te.
b content was adjusted. The above sb content was confirmed by X-ray photoelectron spectroscopy.

Next, a 5i (h film) with a thickness of 1,500 mm was formed on the resulting Sb-Te alloy film, which was the recording layer, by electron beam evaporation.The performance of the recording medium thus created was evaluated as follows. did.

(2) A recording medium prepared using a rectangular polycarbonate plate and a Pyrex glass plate as a substrate was used as a sample.

An AlGaAs laser diode (oscillation wavelength: 8300 nm) was used as a light source, and writing and erasing were performed by irradiating laser light converged to a diameter of 1.4 μm from the substrate side of the recording medium.

The change in the amorphous-crystalline state of the recording layer is achieved by using the fact that the crystalline state generally has a lower light reflectance than the amorphous state. The amount of reflected light when irradiated with oscillation, laser light output 0.1 mW) was measured, and the relative change in reflectance ΔR/R (R: reflectance in crystalline state, ΔR: reflection in amorphous state and crystalline state) was measured. (difference in rate) was determined and used as an index. Note that since the alloy film of the recording medium as produced above is in an intermediate state between amorphous and crystalline, the alloy film is first irradiated with continuous wave laser light to heat it above its melting point and then slowly cooled. It was used after complete crystallization.

The output of the inlaid laser beam was kept constant at 15 ridges, and the seed was irradiated with a laser beam of a pulse width to examine the conditions under which writing was possible under which the relative change in reflectance was 30%. As a result, in the sample of Example, the recording medium whose substrate was a rectangular polycarbonate plate had 3
It was 0 to 70 nsec, and in the case of a recording medium whose substrate was a Pyrex glass plate, it was 60 to 90 nsec.

We attempted to erase the signal written on the plate by changing the output and pulse width of the laser beam, and evaluated the shortest erasable pulse width as the erasing speed. In the samples of the examples, high-speed erasing with a pulse width of 200 nsec or less was possible in all cases.

1 included and Hoshizaya A sample whose substrate is a Pyrex glass plate written on blood is heat treated at various temperatures from room temperature to 250°C, and the written signal is halved by 100 seconds of heat treatment. The temperature was determined and this temperature was defined as the crystallization temperature. the result,
In each case, the crystallization temperature was 120° for the example samples.
It was C or higher. This means that the amorphous state is stable for more than 10 years at room temperature.

Writing was performed on a sample using a Pyrex glass plate as a substrate for ``input'' with a laser beam output of 1511 and a pulse width of 90 nsec, and erasing was performed with a laser beam output of 15 mW and a pulse width of 2.
The writing and erasing operations were repeated at 00 nsec.

As a result, all of the samples of Examples had good reproducibility <1.
It was possible to repeat writing and erasing more than 03 times. When the number of repetitions exceeds 5X10' times, the sb content is 40
Although the samples with atomic % and 70 atomic % could not be completely erased, the samples of other examples still had good reproducibility.

(3) FA and η1 ratio The carrier wave-to-noise ratio (C
/N ratio) was evaluated as follows.

Laser light output during writing 15IIIW, pulse width IQ
Onsec, laser light output during playback 1, 2m
W.

When recording and reproducing experiments were conducted at a disk rotation speed of 180 rpm, the C/N ratio was 55 dB or more in all cases for the samples of the examples.

Subsequently, when the information writing section of the disk was scanned with a laser beam with an output of 6 mW, it was possible to completely erase the written information on the disks of the examples in all cases.

The above writing and erasing process was repeated 10'' times, but in the sample of the example, no decrease in the C/N ratio was observed, and no unerased area was left, allowing for complete erasing.

Example 2 A recording medium was manufactured in the same manner as in Example 1, except that the recording layer and the upper and lower protective layers were formed by RF sputtering. Sputtering for forming the recording layer uses Ar as a sputtering gas, and the gas pressure is 5 x 10-'' Torr, R
The recording was conducted at an F output of 100 W, and the composition of the 5b-Te alloy film serving as the recording layer was adjusted by changing the composition of the 5b-Te alloy serving as the target.

The obtained recording medium was evaluated in the same manner as in Example 1, and results were found to be equivalent to those in Example 1 in all respects: long-term stability of writing conditions, high-speed erasing performance, and repeatability of writing and erasing. Obtained.

〔Effect of the invention〕

The optical recording medium of the present invention satisfactorily combines the required characteristics such as long-term storage of written state, high-speed erasing performance, and repeatability of writing and erasing, which could not be improved at the same time in the past, and is rewritable. It is excellent as a laser beam recording medium.

Agent: Patent attorney Shushi Iwamiya

Claims (2)

[Claims] (1) Formula: Sb_xTe_1_-_x [Here, x is a number of 0.4≦x<0.7. ] An optical recording medium having a recording layer made of an alloy having a composition represented by: (2) The optical recording medium according to claim 1, wherein at least one of the upper surface and the lower surface of the recording layer contains an inorganic oxide, an inorganic nitride, a metal fluoride, a metal sulfide, and an organic polymer. An optical recording medium provided with a protective layer made of at least one substance selected from substances.